The present invention is related to electronic expansion valves (EEVs) employed in refrigeration systems, and in particular to control algorithms used to regulate the position of the EEVs.
Vapor cycle refrigeration systems are commonly employed to provide cooling. A typical vapor cycle refrigeration system includes an evaporator, a compressor and an electronic expansion valve (EEV). Refrigerant is provided to the evaporator in a two-phase state (i.e., a combination liquid-gaseous state), wherein the refrigerant in the evaporator absorbs heat via latent heat transfer through an evaporation process in which the refrigerant is converted to a purely gaseous state. The heated refrigerant provided at an output of the evaporator is received by a compressor. To avoid excessive power demands and/or damage to the compressor, it is important that the refrigerant received by the compressor be in a purely gaseous state. However, to minimize power consumption and maximize the coefficient of performance associated with the system, it is important to minimize the temperature of the refrigerant entering the compressor.
The temperature and state of the refrigerant exiting the evaporator is based, in part, on the flow of refrigerant through the evaporator. The flow of refrigerant through the evaporator is a function of the compressor speed and the position (i.e., opened/closed) of the electronic expansion valve (EEV). If too much refrigerant flow is provided for the amount of heat absorbed in the evaporator, then the refrigerant provided at the output of the evaporator will remain in the liquid state. If insufficient refrigerant flow is provided to the evaporator, then all of the refrigerant will evaporate and will continue to absorb heat within the evaporator, such that the refrigerant provided at the output of the evaporator has a greater than desired temperature.
The electronic expansion valve is used to regulate the flow of refrigerant within the refrigeration circuit such that the refrigerant exiting the evaporator is in the gaseous state, but not above a desired temperature.